It’s thought that Facebook users will see a Spotify icon appear on the left side of their newsfeed, along with the usual icons for photos and events. By clicking on the Spotify icon, users will install the music streaming service on their desktop in the background, and will enable Facebook users to tap into the millions of songs in Spotify’s library.

And to add to the social aspect, the source told Forbes that there will be a feature that will let users listen to music with friends at the same time.

However, it’s worth noting that the service will only be available in countries where Spotify is currently offered, which is Sweden, Norway, Finland, the UK, France, Spain and the Netherlands. Talks are on-going for Spotify to launch in the US too, a market which is pivotal to Spotify’s growth. Reuters quoted Spotify shareholder Sean Parker today as saying he hoped a US launch could happen this summer.

Spotify is already integrated with Facebook Connect, allowing users to see what their Facebook friends are listening to and share playlists and recommend songs.

A Spotify spokesperson told me:

“We have a good relationship with Facebook in that we have done an integration on Facebook Platform that has been valuable in terms of driving engagement with the Spotify service. We’re continuously working together to make the social experience on Spotify the best it can be and welcome relationships with any company looking to innovate by building more social value into the user experience.”

If this rumored collaboration comes to fruition, both companies stand to gain a lot. Spotify will be able to tap into a massive user-base – one that will grow by over 150m more if Spotify is able to launch in the US – and Facebook moves one step closer towards becoming a true social and media hub. Another collaboration between the social network and Warner Bros. enables users to rent movies through Facebook.